1. Field of the Invention
This invention relates to an alloy target which is suitable for use in the manufacture of a magneto-optical recording medium by sputtering.
2. Description of the Prior Art
A magneto-optical memory has been drawing a great deal of attention as it facilitates the erasure and rerecording of information. Single-crystal materials such as garnets, polycrystalline materials such as MrBi and PtCo, or amorphous materials such as alloys of rare earth elements and transition metals are usually employed for manufacturing a magneto-optical memory.
The use of an amorphous alloy comprising a rare earth element or elements and a transition metal or metals, such as Tb-Fe-Co or Gd-Tb-Fe, provides a variety of advantages. For example, it enables the manufacture of a magneto-optical memory which requires only a small amount of energy for recording information, one which is free from any grain-boundary noise, or one which is large and yet is relatively easy to manufacture. A film of such an amorphous alloy is often formed by sputtering, i.e., by causing ions to collide with a target to form a film on a substrate positioned near it.
There are known a variety of materials which can be used for preparing a target. One of them is disclosed in Japanese Laid-Open Patent Specification No. 70550/1987. It has a mixed structure composed of a phase of an intermetallic compound of a rare earth element and a transition metal and a phase of a transition metal alone. This material has a number of advantages including (1) high cracking resistance and (2) uniform composition of a film.
However, it also has a number of drawbacks including the following:
(1) It can be sputtered only at a low speed; PA1 (2) As the angular distribution of the intermetallic materials which is sputtered differs from that of the transition metal, it is only possible to form a film which is greatly different in composition from the target; PA1 (3) Its permeability is so high that only a small magnetic flux leaks from the surface of the target, resulting in a low sputtering efficiency and thereby a low efficiency of use of the target, especially when a magnetron sputtering device is employed; and PA1 (4) The surface of the target has a rapidly changing shape which causes the formation of a film changing in composition with the lapse of time.